Description:
------------
In this testcase the "write" function is not called. If you remove line with "unset", the write function is called properly. If you delete whole foreach cycle and use 
"unset($_SESSION['A']);" instead, the "write" function si also called - as expected. This bug appear only when you call "unset" inside foreach cycle.

My environment: 
MS Windows Server 2003 SE (Windows NT 5.2 build 3790)
Apache/2.0.53 (Win32) PHP/5.0.4

Smilar (but not exactly same) bug is described as #32564, but it is in the No feedback status and there is no way (for me) to change this status. I hope that this "reproduce code" is much better then codes from #32564

I can provide more information if you ask for them.


Reproduce code:
---------------
<?php
function foo(){return(true);}
function read($id){
  return 'A|s:1:"a";B|s:1:"b";';
}
function write($id, $sess_data){
  print "I'm writing this data: $sess_data\n";
  return true;
}
header('Content-Type: text/plain');
session_set_save_handler("foo", "foo", "read", "write", "foo", "foo");
session_start();
print_r($_SESSION);
foreach($_SESSION as $lsKey => $lsVal){
  if($lsKey != 'A'){
    unset($_SESSION[$lsKey]);  //<<<<<<<< if you comment this line, the write function is called properly
  }
}
print_r($_SESSION);
?>

Expected result:
----------------
Array
(
    [A] => a
    [B] => b
)
Array
(
    [A] => a
)
I'm writing this data: A|s:1:"a";


Actual result:
--------------
Array
(
    [A] => a
    [B] => b
)
Array
(
    [A] => a
)